Apparatus for Sensor with Configurable Damping and Associated Methods

ABSTRACT

A sensor includes a coil suspended in a magnetic field, an optical detector to detect displacement of the coil in response to a stimulus, and a feedback circuit coupled to the optical detector and to the coil to drive the coil. The sensor also includes a damping circuit coupled in parallel with the coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is related to the following patent applications:

U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Programmable Gain and Dynamic Range and Associated Methods,” Attorney Docket No. SIAU002;

U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Configurable Coil Constant and Associated Methods,” Attorney Docket No. SIAU003;

U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Communication Port for Configuring Sensor Characteristics and Associated Methods,” Attorney Docket No. SIAU004;

U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Improved Power Consumption and Associated Methods,” Attorney Docket No. SIAU005;

U.S. patent application Ser. No. ______, filed on ______, titled “Apparatus for Sensor with Configurable Coil and Associated Methods,” Attorney Docket No. SIAU006; and

International Application No. PCT/US2013/032584, filed on Mar. 15, 2013, titled “Closed Loop Control Techniques for Displacement Sensors with Optical Readout.” The foregoing applications are incorporated by reference in their entireties for all purposes.

Furthermore, the present patent application is a continuation-in-part of International Application No. PCT/US2013/032584, filed on Mar. 15, 2013, titled “Closed Loop Control Techniques for Displacement Sensors with Optical Readout,” which claims priority to: (1) Provisional U.S. Patent Application No. 61/712,652, filed on Oct. 11, 2012; and (2) Provisional U.S. Patent Application No. 61/721,903, filed on Nov. 2, 2012. The foregoing applications are incorporated by reference in their entireties for all purposes.

TECHNICAL FIELD

The disclosure relates generally to sensors, such as acceleration, speed, and displacement sensors and, more particularly, to apparatus for such sensors with configurable damping, and associated methods.

BACKGROUND

With advances in electronics, a variety of sensors have been developed to sense physical quantities. The sensors may use a variety of technologies, such as electrical, mechanical, optical, and micro-electromechanical systems (MEMS), or combinations of such technologies. More particularly, some sensors can sense displacement, velocity, or acceleration. Sensors that can sense displacement, velocity, or acceleration find use in a variety of fields, such as ground or earth exploration, for instance, reflection seismology.

As an example, devices known as geophones use a magnet and a coil that move relative to each other in response to ground movement. Waves sent into the earth generate reflected energy waves. In response to reflected energy waves, geophones generate electrical signals that may be used to locate underground objects, such as natural resources.

FIG. 1 illustrates a conceptual diagram 10 of a geophone, which includes a magnet 16 coupled to an anchor point 12 (e.g., housing) and spring 14, and coil 18 with mass m. In response to a stimulus, such as the energy waves described above, coil 18 moves in relation to magnet 16. As a result, an electrical output signal is generated by coil 18.

The coil-spring assembly form a physical system that responds non-uniformly as the frequency of the stimulus is varied. Assuming that spring 14 has a spring constant k, the coil-spring assembly, with mass m (i.e., a negligible spring mass), has a natural frequency of oscillation of

$f_{N} = {\sqrt{\frac{k}{m}}.}$

FIG. 2 illustrates a frequency response curve 20 of the geophone of FIG. 1 to physical stimuli. Frequency response curve 20 has a peak 23 at the frequency f_(N). Thus, geophone 10 has better response (higher output signal level) at frequencies near or equal to f_(N).

Note that the description in this section and the corresponding figures are included as background information material. The materials in this section should not be considered as an admission that such materials constitute prior art to the present patent application.

SUMMARY

According to an exemplary embodiment, a sensor includes a coil suspended in a magnetic field, an optical detector to detect displacement of the coil in response to a stimulus, and a feedback circuit coupled to the optical detector and to the coil to drive the coil. The sensor also includes a damping circuit coupled in parallel with the coil.

According to another exemplary embodiment, a system includes a sensor. The sensor includes a coil suspended in a magnetic field, an optical detector to detect displacement of the coil in response to a stimulus, and a feedback circuit coupled to the optical detector and to the coil to drive the coil. The sensor further includes a damping circuit coupled in parallel with the coil to provide damping during shipment, handling, installation, or operation of the sensor.

According to another exemplary embodiment, a method of operating a sensor is disclosed. The sensor includes a coil suspended in a magnetic field, an optical detector to detect displacement of the coil in response to a stimulus, a feedback circuit coupled to the optical detector and to the coil to drive the coil, and a damping circuit coupled in parallel with the coil. The method includes damping the sensor using the damping circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings illustrate only exemplary embodiments and therefore should not be considered as limiting the scope of the application or the claims. Persons of ordinary skill in the art appreciate that the disclosed concepts lend themselves to other equally effective embodiments. In the drawings, the same numeral designators used in more than one drawing denote the same, similar, or equivalent functionality, components, or blocks.

FIG. 1 illustrates a conceptual diagram of a geophone.

FIG. 2 depicts the frequency response of a geophone in response to physical stimuli.

FIG. 3 shows a sensor according to an exemplary embodiment.

FIG. 4 depicts forces operating in a sensor according to an exemplary embodiment.

FIG. 5 illustrates a virtual spring caused by use of negative feedback in an exemplary embodiment.

FIG. 6 depicts a cross-section of a sensor according to an exemplary embodiment.

FIG. 7 illustrates a cross-section of a sensor according to an exemplary embodiment.

FIG. 8 shows a schematic diagram of a sensor according to an exemplary embodiment.

FIG. 9 illustrates a schematic diagram of a sensor according to an exemplary embodiment.

FIG. 10 depicts an output signal of a trans-impedance amplifier (TIA) in an exemplary embodiment.

FIG. 11 shows a flow diagram for a method of operating a sensor according to an exemplary embodiment.

FIG. 12 illustrates a block diagram of a sensor communicating with another device or component according to an exemplary embodiment.

FIG. 13 depicts a circuit arrangement for a sensor with a damping circuit according to an exemplary embodiment.

FIG. 14 illustrates a circuit arrangement for a sensor with a damping circuit according to another exemplary embodiment.

FIG. 15 shows a circuit arrangement for a sensor with a damping circuit according to another exemplary embodiment.

FIG. 16 depicts a circuit arrangement for a sensor with a damping circuit according to another exemplary embodiment.

FIG. 17 illustrates a circuit arrangement for a sensor with a damping circuit according to another exemplary embodiment.

FIG. 18 shows a circuit arrangement for a sensor with a damping circuit according to another exemplary embodiment.

FIG. 19 depicts a plot of current-voltage characteristics for a damping circuit used in an exemplary embodiment.

FIG. 20 illustrates a circuit arrangement for using a damping circuit as a variable resistor according to an exemplary embodiment.

DETAILED DESCRIPTION

The disclosed concepts relate generally to sensors, such as acceleration, speed, and displacement sensors. More specifically, the disclosed concepts provide systems, apparatus, and methods for sensors with sensors with configurable damping.

Sensors according to exemplary embodiments can sense acceleration, velocity, and/or displacement. As persons of ordinary skill in the art understand, acceleration, velocity, and displacement are governed by mathematical relationships. Thus, one may sense one of acceleration, velocity, and displacement, and derive the others from it.

For example, if acceleration, a, is sensed, velocity, v, and displacement, x, may be derived from a. More specifically:

$a = {\left. \frac{v}{t}\Rightarrow v \right. = {\int{a \cdot {t}}}}$ $v = {\left. \frac{x}{t}\Rightarrow x \right. = {\int{v \cdot {t}}}}$

Sensors according to exemplary embodiments include a combination of electrical, optical, and mechanical components. FIG. 3 illustrates a conceptual diagram of a sensor 100 according to an exemplary embodiment.

Referring to FIG. 3, sensor 100 includes a spring 106 attached (e.g., at one end) to an acceleration reference frame or plane 103. Spring 106 has a spring constant k_(s). Spring 106 is also attached (e.g., at another end) to coil 109. Coil 109 and its corresponding assembly (not shown), e.g., a bobbin, have a mass m, also known as proof mass.

A magnet 112 is positioned near or proximately to coil 109. A magnetic field 112A is established between the north and south poles of magnet 112. Thus, coil 109 is completely or partially suspended within magnetic field 112A. By virtue of spring 106, coil 109 may move in relation to magnet 112 and, thus, in relation to magnetic field 112A.

More specifically, in response to a physical stimuli, such as a force that causes displacement x of coil 109, coil 109 moves in relation to magnet 112 and magnetic field 112A. As persons of ordinary skill in the art understand, movement of a conductor, such as coil 109, in a magnetic field, such as magnetic field 112A, induces a current in the coil. Thus, in response to the stimuli, coil 109 produces a current.

Optical position sensor 115 detects the movement of coil 109 in response to the stimuli. More specifically, as described below in detail, optical position sensor 115 generates an output signal, for example, a current, in response to the movement of coil 109.

Note that in some embodiments, rather than generating a current, optical position sensor 115 may generate a voltage signal. For example, optical position sensor 115 may include a mechanism, such as an amplifier or converter, to convert a current produced by the electro-optical components of optical position sensor 115 to an output voltage. In either case, optical position sensor 115 provides an output signal 115-1 to amplifier 118.

Without loss of generality, in exemplary embodiments, amplifier 118 constitutes a TIA. TIA 118 generates an output voltage in response to an input current. Thus, in the case where optical position sensor 115 provides an output current (rather than an output voltage) 115-1, TIA 118 converts the current to a voltage signal.

In some embodiments, depending on a number of factors, TIA 118 may include circuitry for driving coil 109, such as a coil driver (not shown). Such factors include design and performance specifications for a given implementation, for example, the amount of drive specified for coil 109, etc., as persons of ordinary skill in the art will understand.

TIA 118 (or other amplifier circuitry, as noted above) provides an output signal 118-1 to coil 109. The polarity of output signal 118-1 is selected such that output signal 118-1 counteracts the current induced in coil 109 in response to the physical stimuli. In other words, optical position sensor 115 and TIA 118 couple to coil 109 so as to form a negative-feedback loop.

The feedback or driving signal, i.e., signal 118-1, causes a force to act on coil 109. In exemplary embodiments, the force is proportional to the displacement x. Thus, a force exerted by spring 106 and a force exerted by coil 109 (by virtue of negative feedback and driving signal 118-1) cooperate with each other against the force created by acceleration of coil 109 (the proof mass). FIG. 4 illustrates the two forces.

More specifically, FIG. 4 shows a force vector 121 that corresponds to force F_(s) exerted by spring 106. FIG. 4 also depicts a force vector 124 that corresponds to force F_(c) exerted by virtue of the acceleration of coil 109. According to Hook's law, force F_(s) relates to displacement x, specifically F_(s)=−k_(s)·x, where, as noted above, k_(s) represents the spring constant of spring 106. In effect, spring 106 resists the displacement in proportion to k_(s).

Furthermore, according to Newton's second law (ignoring any relativistic effects), force F_(c) relates to the mass of coil 109 (including any physical components, such as a bobbin), and to the acceleration that coil 109 experiences as a result of the external stimuli (e.g., the source that causes displacement x to occur). Specifically, F_(c)=m_(c)·a, where m_(c) represents the mass of coil 109, and a denotes the acceleration that coil 109 experiences.

As noted above, negative feedback is employed in sensor 100 (see FIG. 5) so as to cause the mass m_(c) to come to equilibrium. Mathematically stated, the feedback causes the mass m_(c) to come to equilibrium when F_(s) equals F_(c). Thus, sensor 100 may be viewed as operating according to a force-balance principle, i.e., F_(s)=F_(c) at equilibrium.

Stated another way, force-balance occurs when −k_(s)·x=m_(c)·a. One may readily determine the spring constant k_(s) and the mass of coil 109, m_(c) (e.g., by consulting data sheets or controlling manufacturing processes, etc.). Using the values of k_(s) and m_(c) in the above equation, one may determine the acceleration of coil 109 in response to the stimulus, i.e.:

$a = {\frac{{- k_{s}} \cdot x}{m_{c}}.}$

In other words, output signal 118-1 of TIA 118 is proportional to acceleration a. Given acceleration a, velocity v, and displacement x may be determined, by using the mathematical relations described above. (Note also that optical position sensor 115 may also determine displacement x). Thus, sensor 100 may be used to determine displacement (position), velocity, and/or acceleration, as desired.

Using negative feedback provides a number of benefits. First, it flattens or tends to flatten the response of sensor 100 to the stimuli. Second, feedback increases the frequency response of sensor 100, i.e., sensor 100 has more of a broadband response because of the use of feedback.

Third, negative feedback reduces the amount of displacement that results in a desired output signal level. In effect, negative feedback acts as a virtual spring coupled in parallel with spring 106, a concept that FIG. 5 illustrates. More specifically, the negative-feedback signal applied to coil 109 causes virtual spring 130 to counteract force F_(c), which is exerted because of the acceleration of coil 109, as described above. Thus, spring 106 and virtual spring 130 work as additive forces to reach force equilibrium in opposition to the force created by acceleration of the coil mass (proof mass). Virtual spring 130 is controlled electronically, e.g., by TIA 118 in FIG. 3.

Referring again to FIG. 5, because of the use of negative feedback, virtual spring 130 has a larger spring constant, k_(v), than does spring 106. Use of virtual spring 130 results in sensor 100 creating a given output in response to a smaller stimulus. Put another way, virtual spring 130 acts as a stiff spring. Thus, compared to an open-loop arrangement, sensor 100 has a reduced total displacement for a desired level of output signal. Also, force applied to a sensor that uses an open-loop arrangement (e.g., a geophone), causes the mass suspended by the spring to wobble more, which limits the upper response limit of the sensor.

As noted, use of negative feedback flattens or tends to flatten the sensor frequency response, and also reduces the sensitivity of the force-balance system to the value of spring constant k_(s) of spring 106, since the spring constant of virtual spring 130 dominates. A benefit of the foregoing is to allow the use of a stiffer spring suspension 106, which in turn facilitates sensor operation at any orientation with respect to Earth's gravity. Additionally, an increase in loop gain results in a stiffer virtual spring constant 130, which in turn allows a larger full scale stimulus range.

Note that a variety of embodiments of sensors according to the disclosure are contemplated. For example, in some embodiments, the position of coil 109 and magnet 112 may be reversed or switched (see FIG. 3). Thus, coil 109 may be stationary, while magnet 112 may be suspended by spring 106.

As another example, in some embodiments, more than one magnet 112 may be used, as desired. As yet another example, in some embodiments, more than one coil 109 may be used, e.g., two coils in parallel or series, as desired. Other arrangements are possible, depending on factors such as design and performance specifications, cost, available technology, etc., as persons of ordinary skill in the art will understand.

FIG. 6 depicts a cross-section of a sensor 200 according to an exemplary embodiment. Sensor 200 includes a housing, frame, or enclosure 205 to provide physical support for various components of sensor 200. In the embodiment shown, housing 205 has sides 205A, 205B, 205C, and 205D, for example, a top, a right side or wall, a bottom, and a left side or wall. Other housing, frames, or enclosures are possible and contemplated, as persons of ordinary skill in the art will understand.

Magnet 112 is arranged with magnet caps 215A and 215B. In the embodiment shown, magnet 112 is disposed between magnet caps 215A and 215B. A variety of types and shapes of magnets may be used, as desired. Examples include neodymium-iron-boron (NIB) or aluminum nickel cobalt (ALNICO) alloy magnets, but other materials, such as alloys with appropriate properties, may be used. Other arrangements of the magnet and magnet caps or support are possible and contemplated, as persons of ordinary skill in the art will understand.

Coil 109 is wound on a bobbin 220. In the embodiment shown, coil 109 and bobbin 220 together form the proof mass (neglecting the mass of spring 106). In the embodiment shown, coil 109 is wound in two sections on bobbin 220, although other arrangements are possible and contemplated, as persons of ordinary skill in the art will understand.

The proof mass is suspended by spring 106, which for illustration purposes is shown as four sections labeled 106A-106D. In exemplary embodiments, spring 106 may include one, two, or more springs, such as flat, leaf, or spider springs, as desired. Other types and/or arrangements of spring 106 are possible and contemplated, as persons of ordinary skill in the art will understand. A variety of materials and techniques may be used to fabricate spring 106. Some examples include etching or die cutting. Beryllium copper may be used as one example of spring material, but other materials with appropriate spring properties (e.g., having relatively low temperature coefficient) may be used, as desired.

In exemplary embodiments, such as the embodiment of FIG. 6, spring 106 may have a relatively low spring constant. More specifically, spring 106 may have sufficient stiffness to suspend and support the proof mass. As noted above, a virtual spring (not shown) having a relatively high spring constant (i.e., higher than the spring constant of spring 106) operates in conjunction with spring 106. Thus, spring 106 may provide just enough stiffness to physically support the proof mass.

In the embodiment shown in FIG. 6, spring 106 (shown as sections or portions 106A-106D) suspend the proof mass with respect to magnet 112 (and magnet caps 215A-215B, if used). In other words, a stimulus, such as force, applied to sensor 200 causes the proof mass to move or experience a displacement with respect to magnet 112 (and magnet caps 215A-215B). Other arrangements are possible and contemplated, as persons of ordinary skill in the art will understand. For example, spring 106 may attach to housing 205, rather than magnet caps 215A-215B.

Sensor 200 includes an optical interferometer to generate an electrical signal in response to displacement of coil 109 in relation to magnet 112 or housing 205. The electrical signal constitutes the output of the optical interferometer. The electrical signal may be provided to an amplifier, e.g., TIA 118 in FIG. 3.

Referring again to FIG. 6, in the embodiment shown, the optical interferometer includes a light source 225, such as a vertical cavity surface-emitting laser (VCSEL). The light output of light source 225 is reflected by a mirror 222, and is diffracted by diffraction grating 235. The resulting optical signals are detected by optical detectors 230A, 230B, and 230C.

A mechanical or physical stimulus applied to sensor 200 causes a change in the detected light, and thus causes optical detectors 230A-230C to provide an electrical output signal. The electrical output signal, e.g., a current signal, may be used in a feedback loop, as discussed above.

Note that, if desired, the electrical output signal may be used in an open-loop configuration, rather than in a closed-loop (negative feedback) configuration. As noted above, closed-loop configuration provides some advantages over open-loop configuration. In some situations, however, operating sensor 200 in an open-loop configuration may be desired, for instance, on a temporary basis.

FIG. 7 depicts a cross-section of a sensor 250 according to an exemplary embodiment. Sensor 250 includes a housing, frame, or enclosure 205 to provide physical support for various components of sensor 250. In the embodiment shown, housing 205 has sides 205A, 205B and 205C, for example, a right side or wall, a bottom, and a left side or wall. Other housing, frames, or enclosures are possible and contemplated, as persons of ordinary skill in the art will understand.

Magnet 112 is arranged with magnet caps 215A, 215B, and 215C. In the embodiment shown, magnet 112 is attached to magnet cap 215B, which is disposed against or in contact with magnet caps 215A and 215C. A variety of types and shapes of magnets may be used, as desired. As noted, examples include neodymium-iron-boron (NIB) or aluminum nickel cobalt (ALNICO) alloy magnets, but other materials, such as alloys, with appropriate properties can be used. In some embodiments, magnet 112 may extend to a cavity in bobbin 220 (described below). Other arrangements of the magnet and magnet caps or support are possible and contemplated, as persons of ordinary skill in the art will understand.

Coil 109 is wound on a bobbin 220. In the embodiment shown, coil 109 and bobbin 220 together form the proof mass (neglecting the mass of spring 106). In the embodiment shown, coil 109 is wound around bobbin 220, although other arrangements are possible and contemplated, as persons of ordinary skill in the art will understand.

The proof mass is suspended by spring 106, which for illustration purposes is shown as four sections labeled 106A-106D. In exemplary embodiments, spring 106 may include one, two, or more springs, such as flat, leaf, or spider springs, as desired. Other types and/or arrangements of spring 106 are possible and contemplated, as persons of ordinary skill in the art will understand. As noted above, a variety of materials and techniques may be used to fabricate spring 106. Some examples include etching or die cutting. Beryllium copper may be used as one example of spring material, but other materials with appropriate spring properties (e.g., having relatively low temperature coefficient) may be used, as desired.

In exemplary embodiments, such as the embodiment of FIG. 7, spring 106 may have a relatively low spring constant. More specifically, spring 106 may have sufficient stiffness to suspend and support the proof mass. As noted above, a virtual spring (not shown), having a relatively high spring constant (i.e., higher than the spring constant of spring 106) operates in conjunction with spring 106. Thus, spring 106 may provide just enough stiffness to physically support the proof mass.

In the embodiment shown in FIG. 7, spring 106 (shown as sections or portions 106A-106D) suspend the proof mass with respect to magnet 112 (and magnet caps 215A-215C, if used). In other words, a stimulus, such as force, applied to sensor 250 causes the proof mass to move or experience a displacement with respect to magnet 112 (and magnet caps 215A-215C). Other arrangements are possible and contemplated, as persons of ordinary skill in the art will understand. For example, spring 106 may attach to magnet caps 215A and 215C, rather than housing 205.

Sensor 250 includes an optical interferometer to generate an electrical signal in response to displacement of coil 109 in relation to magnet 112 or housing 205. The electrical signal constitutes the output of the optical interferometer. The electrical signal may be provided to an amplifier, e.g., TIA 118 in FIG. 3.

Referring again to FIG. 7, in the embodiment shown, the optical interferometer includes a light source 225, such as a VCSEL. The light output of light source 225 is reflected by a mirror 222, and is diffracted by diffraction grating 235. The resulting optical signals are detected by optical detectors 230A, 230B, and 230C.

A stimulus applied to sensor 250 causes a change in the detected light, and thus causes optical detectors 230A-230C to provide an electrical output signal. The electrical output signal, e.g., a current signal, may be used in a feedback loop, as discussed above.

Note that, if desired, the electrical output signal may be used in an open-loop configuration, rather than in a closed-loop (negative feedback) configuration. As noted above, closed-loop configuration provides some advantages over open-loop configuration. In some situations, however, operating sensor 250 in an open-loop configuration may be desired, for instance, on a temporary basis.

FIG. 8 shows a schematic diagram or circuit arrangement 300A for a sensor according to an exemplary embodiment, for instance sensors 200 and 250 in FIGS. 6 and 7, respectively. Referring to FIG. 8, as described above, optical detectors 230A-230C (photodiodes in the embodiment shown) provide an output signal to TIA 118. A bias source, labeled V_(BIAS), for example, ground or zero potential, provides an appropriate bias signal to detectors 230A-230C. In the embodiment of FIG. 8, the output signal of optical detectors 230A-230C is provided to TIA 118 as a differential signal.

Note that FIG. 8 omits light source 225 for the sake of clarity of presentation. Light source 225, e.g., a VCSEL, may be powered by an appropriate circuit (not shown). Examples include a voltage regulator, a reference source, etc., as desired. Also, in some embodiments, MCU 310 may control or program the light level that light source 225 emits, depending on various factors, such as power consumption, desired sensor parameters and performance, etc.

In the embodiment shown in FIG. 8, TIA 118 includes two individual TIA circuits or amplifiers, 118A and 118B, to accommodate the differential input signal. TIA 118 includes resistors 305A-305B to adjust (or calibrate or set or program or configure) the gain of TIAs 118A-118B, respectively.

Thus, by adjusting resistor 305A, the gain of amplifier 118A may be adjusted. Similarly, by adjusting resistor 305B, the gain of amplifier 118B may be adjusted. A controller, such as a microcontroller unit (MCU) 310 in the exemplary embodiment shown, adjusts the values of resistors 305A-305B.

Typically, given the differential nature of the input signal of TIA 118, MCU 310 adjusts resistors 305A-305B to the same resistance value so as to increase or improve the common-mode rejection ration (CMRR) of TIA 118. Put another way, the two branches of TIA 118, i.e., the branches containing amplifiers 118A and 118B, respectively, are typically matched by adjusting resistors 305A-305B to the same resistance value. In some situations, however, resistors 305A-305B might be adjusted to different values, for example to compensate for component mismatch, manufacturing variations, etc.

Note that adjusting the gains of amplifiers 118A-118B does not set the full-scale range of the sensor. Rather, the gains of amplifiers 118A-118B determine the overload point of the sensor, i.e., the peak overload point of the sensor in response to a stimulus. Furthermore, the coil constant of coil 109 determines the magnitude of the output signal of the sensor in response to a given amount of acceleration in response to a stimulus, such as force. The coil constant is defined in units of Newtons per Ampere. Increasing the coil constant increases the full-scale range of the sensor for a given available or applied coil current. For fixed values of resistors 320A and 320B, the effect of increasing coil constant is a decrease in the sensor's scale factor in terms of Volts per unit of stimulus (e.g., acceleration (g)), as force-balance equilibrium will be reached at a lower coil current (and hence output voltage) for a given stimulus value.

The output of amplifier 118A feeds one end or terminal of coil 109 via resistors 315A and 320A. Conversely, the output of amplifier 118B feeds the other end of coil 109 via resistors 315B and 320B. Thus, amplifiers 118A-118B provide a drive signal for coil 109 via resistors 315A-315B and 320A-320B.

MCU 310 may adjust (or calibrate or set or program or configure) the values of resistors 320A-320B. Similar to resistors 305A-305B, typically, given the differential nature of the output signal of the sensor, MCU 310 adjusts resistors 320A-320B to the same resistance value. In some situations, however, resistors 320A-320B might be adjusted to different values, for example to compensate for component mismatch, manufacturing variations, etc.

Note that the values of resistors 320A-320B affect the gain or scale factor of the sensor. In other words, the values of resistors 320A-320B determine the full range or scale that the sensor can sense, e.g., the full range of acceleration in response to the stimulus.

Nodes 325A and 325B provide the differential output signal of the sensor. In the embodiment shown, node 325A provides the positive output signal, whereas node 325B provides the negative output signal. Together, the positive and negative output signals provide a differential output signal that is proportional to acceleration, a, experienced by the proof mass in response to the stimulus (e.g., force), as discussed above.

In some embodiments, MCU 310 may include circuitry to receive and process the output signal provided at nodes 325A-325B. For example, MCU 310 may include analog-to-digital converter (ADC) circuitry to convert the output signal at nodes 325A-325B to a digital quantity. MCU 310 may communicate the resulting digital quantity to another circuit or component, for example, via link 370, as desired. Furthermore, MCU 310 may receive power (to supply the various components in the sensor) or other information, for example, parameters related to adjusting various resistor values, as described above, via link 370.

FIG. 9 shows a schematic diagram or circuit arrangement 300B for a sensor according to an exemplary embodiment, for instance sensors 200 and 250 in FIGS. 6 and 7, respectively. Referring to FIG. 9, as described above, optical detectors 230A-230C (photodiodes in the embodiment shown) provide an output signal to TIA 118. In the example shown, V_(BIAS) is ground potential although, as noted above, other appropriate values may be used. In the embodiment of FIG. 9, the output signal of optical detectors 230A-230C is provided to TIA 118 as a single-ended signal.

Note that FIG. 9 omits light source 225 for the sake of clarity of presentation. Light source 225, e.g., a VCSEL, may be powered by an appropriate circuit (not shown). Examples include a voltage regulator, a reference source, etc., as desired. Also, in some embodiments, MCU 310 may control or program the light level that light source 225 emits, depending on various factors, such as power consumption, desired sensor parameters and performance, etc.

The gain of TIA 118 may be adjusted by adjusting (or calibrating or setting or programming or configuring) resistor 305. In the embodiment shown, MCU 310 adjusts the values of resistor 305. In other embodiments, other arrangements may be used, as desired, for example, use of a host or controller coupled to the sensor, described below.

The output of TIA 118 drives an input of amplifier 345 via resistor 335. A feedback resistor 340 couples the output of amplifier 345 to resistor 335 (input of amplifier 345). If desired, the gain of amplifier 345 may be adjusted by adjusting resistor 340 (more specifically, the ratio of resistors 340 and 335). In the embodiment shown, MCU 310 may adjust the value of resistor 345.

The output of amplifier 345 drives an input of amplifier 355 via resistor 350. A feedback resistor 360 couples the output of amplifier 355 to resistor 350 (input of amplifier 355). If desired, the gain of amplifier 355 may be adjusted by adjusting resistor 360 (more specifically, the ratio of resistors 360 and 350). In the embodiment shown, MCU 310 may adjust the value of resistor 360.

Note that adjusting the gain of TIA 118 (and optionally the gains of amplifiers 345 and 355) does not set the full-scale range of the sensor. Rather, the gain of TIA 118 (and optionally the gains of amplifiers 345 and 355) determines the overload point of the sensor, i.e., the peak overload point of the sensor in response to a stimulus. Furthermore, the coil constant of coil 109 determines the magnitude of the output signal of the sensor in response to a given amount of acceleration in response to a stimulus, such as force. More specifically, the coil constant of coil 109 in conjunction with the values of 320A and 320B determine the output scale factor in Volts per unit of stimulus, e.g., g of acceleration.

The output of amplifier 345 feeds one end or terminal of coil 109 via resistors 315A and 320A. Conversely, the output of amplifier 355 feeds the other end of coil 109 via resistors 315B and 320B. Thus, amplifiers 345 and 355 provide a drive signal for coil 109 via resistors 315A-315B and 320A-320B.

MCU 310 may adjust (or calibrate or set or program or configure) the values of resistors 320A-320B. Note that the values of resistors 320A-320B affect the gain or scale factor of the sensor. In other words, the values of resistors 320A-320B determine the full range or scale that the sensor can sense, e.g., the full range of acceleration in response to the stimulus.

Nodes 325A and 325B provide the differential output signal of the sensor. In the embodiment shown, node 325A provides the positive output signal, whereas node 325B provides the negative output signal. Together, the positive and negative output signals provide a differential output signal that is proportional to acceleration, a, experienced by the proof mass in response to the stimulus (e.g., force), as discussed above.

In some embodiments, MCU 310 may include circuitry to receive and process the output signal provided at nodes 325A-325B. For example, MCU 310 may include analog-to-digital converter (ADC) circuitry to convert the output signal at nodes 325A-325B to a digital quantity. MCU 310 may communicate the resulting digital quantity to another circuit or component, for example, via link 370, as desired. Furthermore, MCU 310 may receive power (to supply the various components in the sensor) or other information, for example, parameters related to adjusting various resistor values, as described above, via link 370.

Note that although the exemplary embodiments of FIGS. 8-9 show MCU 310 as the controller, other possibilities exist and are contemplated. For example, a processor (e.g., a central processing unit (CPU) or other type of processor), a logic circuit, a finite-state machine, etc., may be used to control the values of the various resistors. The choice of the controller used depends on factors such as design and performance specifications, the degree of flexibility and programmability desired, the available technology, cost, etc., as persons of ordinary skill in the art will understand.

FIG. 10 illustrates the output signal 400 of a TIA 118 in an exemplary embodiment, for example, one of the embodiments of FIGS. 3 and 6-9. Output signal 400 shows how the output signal 400 (measured in Volts) of TIA 118 varies as a function of displacement, x (measured in meters). The output signal 400 shows a variation around a reference point 405 in response to displacement.

Thus, in the example shown, in response to a displacement x₁, having, for example, an absolute value of 100 nm around reference point 405 (say, ±100 nm), the output signal 400 varies from −V to +V, for example, by ±2 volts. The output signal 400 is a function of the gain of TIA 118. As noted above, the gain of TIA 118 determines the peak response or overload point of TIA 118.

Note that the output signal 400 of TIA 118 may be periodic (e.g., a cyclical interference fringe condition) in response to displacement, as persons of ordinary skill in the art will understand. FIG. 10 shows merely a portion of output signal 400 for the sake of discussion.

FIG. 11 shows a flow diagram 500 for a method of operating a sensor according to an exemplary embodiment. More specifically, the figure illustrates the actions that a controller, such as MCU 310, described above, may take, starting with the sensor's power-up.

After power-up, at 505 MCU 310 is reset. The reset of MCU 310 may be accomplished in a variety of ways. For example, a resistor-capacitor combination may hold the reset input of MCU 310 for a sufficiently long time to reset MCU 310. As another example, a power-on reset circuit external to MCU 310 may cause MCU 310 to reset. As another example, MCU 310 may be reset according to commands or control signals from a host.

After reset, MCU 310 begins executing firmware or user program instructions. The firmware or user program instructions may be included in a storage circuit within MCU 310 (e.g., internal flash memory) or in a storage circuit external to MCU 310 (e.g., an external flash memory). In any event, MCU 310 takes various actions in response to the firmware or user program instructions.

At 510, MCU 310 adjusts one or more resistors (e.g., resistors 305A-305B in FIG. 8 or resistor 305 in FIG. 9) to calibrate the gain of TIA 118 (see, for example, FIGS. 8 and 9). As described above in detail, the gain of TIA 118 affects certain attributes of the sensor.

At 515, MCU 310 adjusts resistors (e.g., resistors 320A-320B in FIGS. 8 and 9) in the signal path that drives coil 109 (see, for example, FIGS. 8 and 9). As described above in detail, the values of resistors 320A-320B affects certain attributes of the sensor, such as gain or scale of the sensor. Optionally, MCU 310 may make other adjustments or calibrations, for example, it may adjust the values of resistors 340 and 360 (see FIG. 9).

Referring again to FIG. 11, at 520 MCU 310 may optionally enter a sleep state. In the sleep state certain parts or blocks of MCU 310 may be disabled or powered down or placed in a low-power state (compared to when MCU 310 is powered up). Examples include placing the processor, input/output (I/O) circuits, signal processing circuits (e.g., ADC), and/or other circuits (e.g., arithmetic processing circuits) of MCU 310 in a sleep state.

Placing some of the circuitry of MCU 310 in a sleep state lowers the power consumption of MCU 310, in particular, and of the sensor, overall. Depending on the amount of power consumed in the sleep state and factors such as power-source capacity (e.g., the capacity of a battery used to power the sensor), MCU 310 may remain in the sleep state for relatively long periods of time, e.g., days, weeks, months, or even longer. Thus, the power savings because of the use of the sleep state provide a particular benefit in portable or remote applications where a battery may be used to power the sensor.

Note that some circuitry in MCU 310 may be kept powered up, even during the sleep mode or state. For example, a real-time clock (RTC) circuit (or other timer circuitry) may be kept powered and operational so as to track the passage of time. As another example, interrupt circuitry of MCU 310 may be kept powered and operation so that MCU 310 may respond to interrupts.

As part of entering the sleep state, the state of MCU 310 may be saved, for example, contents of registers, content of the program counter, etc. Saving the state of MCU 310 allows restoring MCU 310 later (e.g., when MCU 310 wakes up or resumes from the sleep state) to the same state as when it entered the sleep state.

MCU 310 may leave the sleep mode or state (wake up) and enter the normal mode of operation (e.g., processing signals generated in the sensor in response to a stimulus), or resume from the sleep state. For instance, in some embodiments, MCU 310 (or a CPU or other processor or controller) remains in the sleep state until one or more conditions are met, for example, the output signal (Out+-Out−) exceeding a preset threshold or value, or a timer generating a signal after a preset amount of time has elapsed, etc. In some embodiments, once the condition(s) is/are met, an interrupt may be generated to cause MCU 310 to leave the sleep state.

As part of the process of leaving the sleep state and entering the normal mode of operation, the state of MCU 310 may be restored (if the state was saved, as described above). Once MCU 310 leaves the sleep state, it can process signals generated in response to the stimuli, as described above.

In some embodiments, the sensor may be self-contained. In other words, the sensor, e.g., MCU 310, may include instructions for code that determine how the sensor responds to stimuli, how it processes the signals generated as a result of the application of the stimulus (e.g., log the signal values, and time/date information, as desired), etc. The sensor may also include a source of energy, such as a battery, to supply power to the various circuits of the sensor. Such embodiments may be suitable for operation in conditions where access to the sensor is limited or relatively difficult.

In other embodiments, the sensor may communicate with another device, component, system, or circuit, such as a host. FIG. 12 illustrates such an arrangement according to an exemplary embodiment.

Specifically, a sensor, such as the sensors depicted in FIGS. 3 and 6-9, includes a controller, such as MCU 310. Circuit arrangement 600 in FIG. 12 also includes a host (or device or component or system or circuit) 605. The sensor, specifically, the controller (MCU 310) communicates with host 605 via link 370.

In exemplary embodiments, link 370 may include a number of conductors, and facilitate performing a number of functions. In some embodiments, link 370 may constitute a multi-conductor cable or other or similar means of coupling. In some embodiments, link 370 may constitute a bus.

In some embodiments, link 370 may constitute a wireless link (e.g., the sensor and host 605 include receiver, transmitter, or transceiver circuitry that allow wireless communication via link 370 by using radio-frequency (RF) signals). Use of a wireless link provides the advantage of communication without using cumbersome electrical connections, and may allow arbitrary or desired locations for the sensor and host 605.

In some embodiments, link 370 may constitute an optical link. Use of an optical link allows for relatively low noise in link 370. In such a situation, the sensor and host 605 may include optical sources and/or receivers or detectors, depending on whether unidirectional or bidirectional communication is desired.

In some embodiments, link 370 provides a mechanism for supplying power to various parts of the sensor. The sensor may include one or more local regulators, as desired, to regulate or convert the power received from host 605 (or other source), for example, by changing the voltage level or increasing the load regulation, as desired.

In some embodiments, link 370 provides a mechanism for the sensor and host 605 to communicate a variety of signals. Examples include data signals, control signals, status signals, and handshaking signals (e.g., as used in information exchange protocols). As an example, link 370 provides a flexible mechanism by which the sensor may receive information (e.g., calibration information) from host 605.

As another example, the sensor may provide information, such as data corresponding to or derived from a stimulus applied to the sensors. Examples of such data include information regarding displacement, velocity, and/or acceleration. Using this mechanism, host 605 may record a log of the data using desired intervals.

In exemplary embodiments, link 370 provides a flexible communication channel by supporting a variety of types of signals, as desired. For example, in some embodiments, link 370 may be used to communicate analog signals. In other embodiments, link 370 may be used to communicate digital signals. In yet other embodiments, link 370 may be used to communicate mixed-signal information (both analog and digital signals).

In some embodiments, host 605 may constitute or comprise an MCU (or other processor or controller) (not shown). In such scenarios, MCU 310 in the sensor may be omitted or may be moved to host 605, as desired. As an alternative, in some embodiments, the MCU in host 605 may communicate with MCU 310 in the sensor.

One aspect of the disclosure relates to sensors with sensors with configurable damping, such as dynamic damping or coil damping. Sensors according to exemplary embodiments include electromechanical or magneto-mechanical components, such as the coil, springs, and magnet. Dynamic damping or coil damping of such systems can immobilize such systems, for instance, to prevent (or reduce the probability of) damage because of shock, vibration, impact, etc.

In the absence of damping, shock, vibration, impact, and the like can cause stress on various sensor components, such as the springs. The stress exerted on the components can cause sensor failure, misalignment, reduced accuracy or performance, and the like.

Damping in sensors according to exemplary embodiments may be used in a number of situations. For example, damping may be used to immobilize or protect the proof-mass during shipment of the sensor, during handling of the sensor, and/or during installation of the sensor.

As another example, damping may be used during operation of the sensor. Consider, for instance, the situation that a sensor is set to a relatively small full-scale range, i.e., a relatively small stimulus, such as acceleration, can produce full-scale output of the sensor. Suppose that a relatively large stimulus is applied to such a sensor. The stimulus can cause the proof-mass to reach the limits of its excursion for normal operation.

In other words, the stimulus can cause an over-range condition of the sensor. Ordinarily, recovery from the over-range condition of the sensor takes a period of time related to the quality factor, or Q, of the electromechanical or magneto-mechanical components of the sensor. If the quality factor is relatively high, recovery from the over-range condition of the sensor can take a relatively long time.

By applying damping to the sensor, the quality factor may be reduced relatively quickly. As a result, the recovery from the over-range condition of the sensor can be accomplished in a shorter time period. Thus, the sensor can resume normal operation more quickly, for example, to respond to the next stimulus.

FIG. 13 depicts a circuit arrangement 650 for a sensor with a damping circuit according to an exemplary embodiment. As described above, the sensor in FIG. 13 includes coil 109 suspended in the magnetic field of one or more magnets 112. Optical position sensor 115 detects the movement of coil 109 in response to stimuli, such as acceleration.

As described above, optical position sensor 115 generates an output signal, for example, a current or voltage, in response to the movement of coil 109. Signal processing circuit 655 is coupled to coil 109 and optical position sensor 115 to form a negative feedback circuit, as described above. Thus, signal processing circuit 655 receives the output signal of optical position sensor 115, processes that signal, and then applies an output signal to coil 109, as described above.

Signal processing circuit 655 may include a variety of components, blocks, or circuits. FIGS. 8-9 show examples according to two exemplary embodiments. Thus, signal processing circuit 655 may include one or more TIAs (not shown), resistors (not shown), amplifiers (not shown), filtering or feedback circuits/networks, etc. Generally, a variety of signal processing circuits 655 are contemplated, and are not limited to the examples shown in FIGS. 8-9, as persons of ordinary skill in the art will understand.

An output of signal processing circuit 655 couples to and drives coil 109. By virtue of the negative feedback in the circuit, coil 109 produces a force such that the sensor operates according to a force-balance principle, as described above.

Damping circuit 665 also couples to coil 109. Specifically, damping circuit 665 is coupled in parallel with coil 109. Damping circuit 665 can provide damping to various components of the sensor, as described above.

Controller 660 couples to damping circuit 665, and controls its operation. In other words, controller 660 can cause damping circuit 665 to apply damping or, conversely, to stop or reduce damping. A variety of types of controller 660 are contemplated. The internal structure of controller 660 depends on the type of damping circuit 665 in a given implementation. Typically, controller 660 includes one or more of voltage or current sources, biasing networks, switches, transistors, resistors, and the like.

In addition to controlling damping circuit 665, controller 660 may perform other functions, as desired. For example, in some embodiments, controller 660 may detect over-range conditions of the sensor, as described above. If it detects such a condition, controller 660 can cause damping circuit 665 to apply damping to the sensor to cause the sensor to recover from the over-range condition and revert to normal operation.

In exemplary embodiments, a variety of structures and circuit arrangements are contemplated for providing damping. FIG. 14 illustrates a circuit arrangement 670 for a sensor with a damping circuit 665 according to another exemplary embodiment.

In the embodiment of FIG. 14, damping circuit 665 includes a controllable switch. Switch 665 has open and closed conditions or states. Controller 660 controls the state of switch 665.

In the embodiment shown, switch 665 is a normally closed controllable switch. In other words, in the absence of a control signal from controller 660, switch 665 is closed. As a result, it shorts or effectively shorts (depending on the on-state or parasitic resistance of switch 665) coil 109, which applies damping to the coil and, hence, to the sensor.

As noted above, damping, as provided by switch 665, may be used to immobilize or protect the proof-mass during shipment of the sensor, during handling of the sensor, and/or during installation of the sensor. Furthermore, damping may be used if an over-range condition of the sensor occurs, for instance, in response to a relatively large amount of acceleration applied to the sensor during its operation.

During normal operation of the sensor (e.g., no damping desired), however, controller 660 causes switch 665 to be open. In its open state, switch 665 has virtually no or negligible effect on the operation of the sensor (assuming sufficiently low leakage of switch 665, such that the leakage current does not affect the operation of the sensor).

FIG. 15 shows a circuit arrangement 680 for a sensor with a damping circuit 665 according to another exemplary embodiment. In the embodiment of FIG. 15, damping circuit 665 constitutes a depletion-mode field-effect transistor (FET).

As a depletion-mode FET, transistor 665 conducts when the voltage applied across its source and gate is zero (V_(GS)=0). Controller 660 controls the state of transistor 665. During normal operation of the sensor (e.g., no damping desired), controller 660 provides a control signal across the source and gate of transistor 665 in order to turn off transistor 665. In its off state, transistor 665 has virtually no or negligible effect on the operation of the sensor (assuming relatively low leakage of transistor 665 so that the leakage current does not affect the operation of the sensor).

On the other hand, when the controller applies no signal across the gate and source of transistor 665, transistor 665 is in the on state, and conducts. In other words, in the absence of a control signal from controller 660 (e.g., V_(GS)=0), transistor 665 is in the on state. As a result, transistor 665 shorts or effectively shorts (depending on the on-state or parasitic resistance of transistor 665) coil 109, which applies damping to the coil and, hence, to the sensor.

As noted above, damping, as provided by transistor 665, may be used to immobilize or protect the proof-mass during shipment of the sensor, during handling of the sensor, and/or during installation of the sensor. Furthermore, damping may be used if an over-range condition of the sensor occurs, for instance, in response to a relatively large amount of acceleration applied to the sensor during its operation.

FIG. 16 depicts a circuit arrangement 690 for a sensor with a damping circuit 665 according to another exemplary embodiment. In the embodiment of FIG. 16, damping circuit 665 constitutes a junction FET (JFET).

A JFET, such as transistor 665, conducts when the voltage applied across its source and gate is zero (V_(GS)=0). Controller 660 controls the state of transistor 665. During normal operation of the sensor (e.g., no damping desired), controller 660 provides a control signal across the source and gate of transistor 665 in order to turn off transistor 665. In its off state, transistor 665 has virtually no or negligible effect on the operation of the sensor (assuming relatively low leakage of transistor 665, such as the leakage current does not affect the operation of the sensor).

Conversely, when the controller applies no signal across the gate and source of transistor 665, transistor 665 is in the on state, and conducts. Thus, in the absence of a control signal from controller 660 (e.g., V_(GS)=0), transistor 665 is in the on state. As a result, transistor 665 shorts or effectively shorts (depending on the on-state or parasitic resistance of transistor 665) coil 109, which applies damping to the coil and, hence, to the sensor.

As noted above, damping, as provided by transistor 665, may be used to immobilize or protect the proof-mass during shipment of the sensor, during handling of the sensor, and/or during installation of the sensor. Furthermore, damping may be used if an over-range condition of the sensor occurs, for instance, in response to a relatively large amount of acceleration applied to the sensor during its operation.

FIG. 17 illustrates a circuit arrangement 700 for a sensor with a damping circuit 665 according to another exemplary embodiment. In the embodiment shown in FIG. 17, damping circuit 665 constitutes a latching relay.

Latching relay 665, such as Omron model 653-G6KU-2P-YDC12 relay, constitutes a bi-stable switch that is electrically controllable. In the embodiment shown, latching relay 665 includes coil 665-1 and contacts 665-2. Contacts 665-2 can have one of two bi-stable states (open, closed) in response to current applied to coil 665-1.

The application of current typically occurs in the form of a pulse or for a short duration. Once latching relay changes state, application of current may be removed. In the absence of coil current, latching relay 665 keeps its state.

Controller 660 can cause the latching relay to operate in either of its two states. During normal operation of the sensor (e.g., no damping desired), controller 660 provides a control signal to latching relay 665 in order to open contacts 665-2. In this state, latching relay 665 has virtually no or negligible effect on the operation of the sensor (assuming no leakage in latching relay 665, or leakage that is small enough so as not to affect the operation of the sensor).

Conversely, when damping is desired, controller 660 provides a control signal to latching relay 665 in order to close contacts 665-2. As a result, latching relay 665 shorts or effectively shorts (depending on the on-state or parasitic resistance of contacts 665-2) coil 109, which applies damping to the coil and, hence, to the sensor.

As noted above, damping, as provided by latching relay 665, may be used to immobilize or protect the proof-mass during shipment of the sensor, during handling of the sensor, and/or during installation of the sensor. Furthermore, damping may be used if an over-range condition of the sensor occurs, for instance, in response to a relatively large amount of acceleration applied to the sensor during its operation.

Note that use of latching relay 665 entails an orderly shut-down sequence for the sensor. Specifically, before the sensor is shut down or powered off, controller 660 causes latching relay 665 to close contacts 665-2, i.e., short or effectively short coil 109. In this state of latching relay 665, damping is applied to coil 109 and, hence, to the sensor, as described above.

In exemplary embodiments, controller 660 provides control signals with appropriate level, polarity, and duration. The characteristics of the control signals depend on the type of damping circuit 665 used in a particular embodiment.

For example, in situations where damping circuit 665 constitutes a latching relay, controller 660 would provide signals with appropriate polarity, level, and duration (depending on the characteristics of the particular latching relay used) to cause the latching relay to switch states, as desired. As another example, in cases where damping circuit 665 constitutes a transistor, such as a depletion-mode FET or JFET, controller 660 provides gate-source voltages (V_(GS)) with appropriate level, polarity, and duration such that the transistor has a desired state (on, off).

Ultimately, the control signals are derived from the power source for the sensor, for example, a battery. Typical batteries have relatively small voltages. In some situations, the output voltage of the battery might not have the appropriate level or polarity to control damping circuit 665.

For instance, transistors, such as a depletion-mode FET or JFET, may be of the p-channel or n-channel types. Furthermore, the transistor might have threshold voltages that the power supply cannot directly exceed (e.g., to turn the transistor off), or the desired signals might have a polarity opposite of what controller 660 can provide.

In such situations, a power supply circuit may be used to derive appropriate voltage levels from the sensor's main power supply (e.g., a battery). FIG. 18 shows a circuit arrangement 710 for a sensor with a damping circuit 665 and a power supply 715 according to an exemplary embodiment. Note that although FIG. 18 shows power supply 715 as a separate circuit block external to controller 660, in some embodiments, power supply 715 may reside in controller 660, as desired.

Power supply 715 receives a supply voltage, V_(DD) (e.g., the battery voltage). Power supply 715 derives one or more voltages of desired or appropriate polarity and/or level to drive damping circuit 665.

Consider as an example the situation where damping circuit 665 includes an n-channel depletion-mode FET. Such a transistor conducts with a gate-source voltage of zero. To turn off the transistor, power supply 715 provides a negative voltage across the gate and source of the transistor. In other situations, turning off a transistor might entail providing a gate-source voltage larger than the supply voltage, V_(DD).

In such situations, power supply 715 provides the desired output signal (e.g., V_(GS)) with appropriate level and/or polarity. In exemplary embodiments, power supply 715 may constitute a charge pump. Given that FET transistors do not conduct appreciable gate current (e.g., relatively small leakage currents), the charge pump provides relatively small output currents. As a result, the charge pump may be implemented with relatively small cost and area or volume.

In exemplary embodiments, controller 660 controls power supply 715. In some embodiments, controller 660 may cause power supply 715 (e.g., a charge pump) to turn off and on, as appropriate, to control damping circuit 665 (e.g., change transistor or relay states, as discussed above). Such an arrangement may help reduce power consumption of the sensor, albeit at the cost of the time it takes power supply 715 to power up or power down.

In some embodiments, power supply 715 may stay on, but controller 660 may gate (e.g., using one or more switches) the output of power supply 715 (e.g., a charge pump). As noted above, when damping circuit 665 uses a FET, the gate current of the FET is relatively small. As a result, power supply 715 provides a relatively small output current, and leaving it on may not impact the overall power consumption of the sensor in an appreciable manner.

In exemplary embodiments where damping circuit 665 uses a FET, controller 660 typically causes the FET to turn on or to turn off, i.e., act effectively as a switch. FIG. 19 depicts a plot 750 of current-voltage characteristics for a FET used in an exemplary embodiment. As plot 750 shows, when turned on, the FET has two modes of operation.

Specifically, the FET can operate in linear region 755 or in saturation region 760. In saturation region 760, the FET acts essentially as a switch. Thus, controller 660 causes the FET to turn on or off, as desired, to provide damping, as discussed above.

In linear region 755, however, the FET exhibits linear or nearly linear characteristics. More specifically, depending on factors such as the voltage across coil 109, in this region, the FET's drain current, i_(D), varies linearly or nearly linearly as a function of the FET's drain-source voltage (v_(DS)).

This property of the FET may be used to provide a variable resistance across coil 109 of the sensor. (Note that even when the FET is used as a variable resistance, it may be turned fully on or off (by changing the gate-source voltages (V_(GS))) to provide damping, as discussed above.) FIG. 20 illustrates a circuit arrangement 770 according to an exemplary embodiment that uses the FET as a variable resistance across coil 109.

More specifically, variable resistor 665 (the FET operating in the linear region) is coupled in parallel with coil 109. Resistor 665 may be varied (configured, trimmed, programmed, modified, adjusted, calibrated, etc.). The output current provided by signal processing circuit 655 gets divided into two currents, one of which flows into coil 109, and another into resistor 665.

By varying resistor 665, the coil constant of the sensor may be changed, which in turn causes changes in sensor attributes such as full-scale range of the sensor. More specifically, assuming a constant output current of signal processing circuit 655, if the resistance of resistor 665 is reduced, more current flows into resistor 665, and less current flows into coil 109. Consequently, the coil constant of the sensor is reduced.

Conversely, if the resistance of resistor 665 is increased, less current flows into resistor 665, but more current flows into coil 109. As a result, the sensor's coil constant is increased. In the limit, i.e., as the resistance of resistor 665 is increased towards infinity (i.e., the FET is turned off), all or virtually all of the output current of signal processing circuit 655 flows into coil 109. In that situation, the coil constant of the sensor is maximized (for a given configuration of the sensor, e.g., the amount of current that signal processing circuit 655 provides).

Operation of the FET in the linear region depends in part on the FET's threshold voltage, V_(T). In some situations, the threshold voltage may lack uniformity across transistors. For example, FETs with the same part number might exhibit differing threshold voltages. To compensate for such variations, the FET might be characterized using a calibration procedure to determine its characteristics, such as V_(T).

The FET's characteristics may be stored (e.g., in non-volatile memory, such as flash memory) in the sensor or elsewhere. The operation of the sensor, such as operating the FET in the linear region to configure the sensor's coil constant, may then be controlled using the stored characteristics.

Configuring the sensor's coil constant using this technique may be used in a variety of situations. For example, configuration of coil constant may occur during manufacture of the sensor, or after manufacture of the sensor, for instance during field use, use by an end-user, etc. As another example, configuration of the coil constant using this technique may be used for configuring or changing the full-scale range of the sensor (e.g., auto-ranging). Configuration of coil constant may occur as often as desired, ranging from once (e.g., during manufacture of the sensor) to more than once (e.g., during use of sensor, periodically, or at desired times, intervals, etc.).

In the embodiments shown, controller 660 controls damping circuit 665 and/or power supply 715. Other arrangements, however, are contemplated and may be used. For example, a controller, either in the sensor or in a remote location (e.g., a remote host, such as host 605 in FIG. 12) may control damping circuit 665 and/or power supply 715.

As another example, MCU 310 (see, for example, FIGS. 8-9) may be used to control damping circuit 665 and/or power supply 715. In some embodiments, MCU 310 may include information, such as instructions or commands, to control damping circuit 665 and/or power supply 715. In some embodiments, MCU 310 may obtain information (e.g., from host 605 or another source), such as instructions or commands, to control damping circuit 665 and/or power supply 715.

Although sensors according to exemplary embodiments have been described and illustrated in the accompanying drawings, a variety of other embodiments and arrangements are contemplated. The following description provides some examples.

In some embodiments, MCU 310 may be omitted. Instead, a remote host, device, component, system, circuit, etc., may couple to circuitry in the sensor to perform various operations, e.g., adjust the values of the various resistors. The sensor may include circuitry to facilitate communication with the remote host. Analog, digital, or mixed-signal control communication signals may be used to adjust the resistor values, as desired.

In some embodiments, the electrical components (e.g., MCU 310, TIA 118, etc.) and rest of the sensor components (e.g., coil, optical position sensor) reside in the same housing. In other embodiments, the electrical components and rest of the sensor components reside in different components (e.g., to allow easier access to some components, while protecting other components) of the same housing.

In yet other embodiments, the electrical components and rest of the sensor components, for example, the coil and/or optical position sensor, reside in different or separate housings. The choice of configuration depends on a variety of factors, as persons of ordinary skill in the art will understand. Examples of such factors include design and performance specifications, the intended physical environment of the sensor, the level of access desired to various components, cost, complexity, etc.

Sensors according to exemplary embodiments may be used in a variety of applications. For example, sensors according to some embodiments may be used for geological exploration. As another example, sensors according to some embodiments may be used for detecting seismic movement, i.e., in seismology. As another example, sensors according to some embodiments may be used for detecting and/or deriving various quantities related to navigation, i.e., in inertial navigations. Other applications include using the sensor as a reference sensor for motion stimulus testing of other components or sensors under test.

Referring to the figures, persons of ordinary skill in the art will note that the various blocks shown might depict mainly the conceptual functions and signal flow. The actual circuit implementation might or might not contain separately identifiable hardware for the various functional blocks and might or might not use the particular circuitry shown. For example, one may combine the functionality of various blocks into one circuit block, as desired. Furthermore, one may realize the functionality of a single block in several circuit blocks, as desired. The choice of circuit implementation depends on various factors, such as particular design and performance specifications for a given implementation. Other modifications and alternative embodiments in addition to those described here will be apparent to persons of ordinary skill in the art. Accordingly, this description teaches those skilled in the art the manner of carrying out the disclosed concepts, and is to be construed as illustrative only. Where applicable, the figures might or might not be drawn to scale, as persons of ordinary skill in the art will understand.

The forms and embodiments shown and described should be taken as illustrative embodiments. Persons skilled in the art may make various changes in the shape, size and arrangement of parts without departing from the scope of the disclosed concepts in this document. For example, persons skilled in the art may substitute equivalent elements for the elements illustrated and described here. Moreover, persons skilled in the art may use certain features of the disclosed concepts independently of the use of other features, without departing from the scope of the disclosed concepts. 

1. A sensor, comprising: a coil suspended in a magnetic field; an optical detector to detect displacement of the coil in response to a stimulus; a feedback circuit coupled to the optical detector and to the coil to drive the coil; and a damping circuit coupled in parallel with the coil.
 2. The sensor according to claim 1, wherein the damping circuit comprises a field effect transistor (FET).
 3. The sensor according to claim 2, wherein the FET comprises a depletion-mode FET.
 4. The sensor according to claim 2, wherein the FET comprises a junction FET (JFET).
 5. The sensor according to claim 1, wherein the damping circuit comprises a latching relay.
 6. The sensor according to claim 1, wherein the damping circuit comprises a normally closed controllable switch.
 7. The sensor according to claim 1, further comprising a controller coupled to control the damping circuit.
 8. The sensor according to claim 7, wherein the controller comprises a microcontroller unit (MCU).
 9. The sensor according to claim 1, further comprising a power supply circuit coupled to a supply of the sensor, the power supply circuit further coupled to provide power to the damping circuit.
 10. The sensor according to claim 9, wherein the power supply circuit comprises a charge pump.
 11. The sensor according to claim 1, wherein the damping circuit comprises a transistor operated in a linear region to configure a coil constant of the sensor.
 12. A system, comprising: a sensor, comprising: a coil suspended in a magnetic field; an optical detector to detect displacement of the coil in response to a stimulus; a feedback circuit coupled to the optical detector and to the coil to drive the coil; and a damping circuit coupled in parallel with the coil to provide damping during shipment, handling, installation, or operation of the sensor.
 13. The system according to claim 12, wherein the damping circuit comprises a depletion-mode field effect transistor (FET) or a junction FET (JFET).
 14. The system according to claim 12, wherein the damping circuit comprises a latching relay.
 15. The system according to claim 12, further a host, wherein the sensor further comprises a controller to control the damping circuit in accordance with information received from the host.
 16. A method of providing damping to a sensor, the sensor including a coil suspended in a magnetic field, an optical detector to detect displacement of the coil in response to a stimulus, a feedback circuit coupled to the optical detector and to the coil to drive the coil, and a damping circuit coupled in parallel with the coil, the method comprising damping the sensor using the damping circuit.
 17. The method according to claim 16, wherein the damping circuit comprises a depletion-mode field effect transistor (FET) or a junction FET (JFET).
 18. The method according to claim 16, wherein the damping circuit comprises a latching relay.
 19. The method according to claim 16, wherein the damping circuit comprises a normally closed controllable switch.
 20. The method according to claim 16, wherein damping the sensor further comprises using information received from a host to control the damping circuit. 